BIOMECHANICS Flashcards
VELOCITY
displacement/time
Velocity of a body only changes if an unbalanced force acts on it.
newtons 2nd law
F=ma acceleration is for the body’s centre of mass (CoM). Different parts of the body may have different velocities and accelerations.
momentum
p=mv (kg.m.s-1),
thus force is the rate of change of momentum.
Weight
Weight = mg (newton, N),
weight of a body is the force exerted on it by gravity Where g is assumed to be 9.81 m.s-1
Statics
deals with the equilibrium of bodies. This applies to bodies at rest or in uniform motion when forces and moments do not generate acceleration (i.e. ∑F = 0, ∑M = 0)
Dynamics
Dynamics is concerned with accelerated motion of bodies
work
is done when forces move their points of application W = F.s
Units of J, joules
Power
is the rate of doing work
P = F.s/t = F.u Units of J.s-1, W, watts
potential energy
Lifting a body of mass m through a height of h requires work mgh(J) and increases its gravitational potential energy
P.E. = mgh (J)
kinetic energy
A mass m moving with velocity u has kinetic energy K.E. = 0.5mu2 (J)
walking gait
Gravitational acceleration, g, acts on our centre of mass which moves in the arc of a circle with a radius equal to lower limb length, h, hence
g = u2/h
umax = √gh
Freely chosen speed
≈ 1.2– 1.4 m.s-1
We use an inverted pendulum principle where: mgh and 1⁄2mu2 are 180˚ out- of-phase
(walking faster or slower = forced pendulum)
when walking
KE and GPE are out-of-phase
Max transfer b/w KE and PE is when Froude number (u2/gh) = 0.25 ~60-70% energy of the centre of mass (COM) is conserved in walking
joint moment
Muscles generate force that results in a joint moment
Moment )torque) = f.d (Nm)
Moment arm (d )
= perpendicular distance from the axis of rotation to the line of action of force.
muscle insertion
Consider the importance of muscle insertion sites in relation to the ‘strength versus speed’ of movement…..
